1NANOSLEEP(2) Linux Programmer's Manual NANOSLEEP(2)
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6 nanosleep - high-resolution sleep
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9 #include <time.h>
10 int nanosleep(const struct timespec *req, struct timespec *rem);
12 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
14 nanosleep(): _POSIX_C_SOURCE >= 199309L
16
18 nanosleep() suspends the execution of the calling thread until either
19 at least the time specified in *req has elapsed, or the delivery of a
20 signal that triggers the invocation of a handler in the calling thread
21 or that terminates the process.
22 If the call is interrupted by a signal handler, nanosleep() returns -1,
24 sets errno to EINTR, and writes the remaining time into the structure
25 pointed to by rem unless rem is NULL. The value of *rem can then be
26 used to call nanosleep() again and complete the specified pause (but
27 see NOTES).
28 The structure timespec is used to specify intervals of time with
30 nanosecond precision. It is defined as follows:
31 struct timespec {
33 time_t tv_sec; /* seconds */
34 long tv_nsec; /* nanoseconds */
35 };
36 The value of the nanoseconds field must be in the range 0 to 999999999.
38 Compared to sleep(3) and usleep(3), nanosleep() has the following
40 advantages: it provides a higher resolution for specifying the sleep
41 interval; POSIX.1 explicitly specifies that it does not interact with
42 signals; and it makes the task of resuming a sleep that has been inter‐
43 rupted by a signal handler easier.
44
46 On successfully sleeping for the requested interval, nanosleep()
47 returns 0. If the call is interrupted by a signal handler or encoun‐
48 ters an error, then it returns -1, with errno set to indicate the
49 error.
50
52 EFAULT Problem with copying information from user space.
53 EINTR The pause has been interrupted by a signal that was delivered to
55 the thread. The remaining sleep time has been written into *rem
56 so that the thread can easily call nanosleep() again and con‐
57 tinue with the pause.
58 EINVAL The value in the tv_nsec field was not in the range 0 to
60 999999999 or tv_sec was negative.
61
63 POSIX.1-2001.
64
66 If the interval specified in req is not an exact multiple of the granu‐
67 larity underlying clock (see time(7)), then the interval will be
68 rounded up to the next multiple. Furthermore, after the sleep com‐
69 pletes, there may still be a delay before the CPU becomes free to once
70 again execute the calling thread.
71 The fact that nanosleep() sleeps for a relative interval can be prob‐
73 lematic if the call is repeatedly restarted after being interrupted by
74 signals, since the time between the interruptions and restarts of the
75 call will lead to drift in the time when the sleep finally completes.
76 This problem can be avoided by using clock_nanosleep(2) with an abso‐
77 lute time value.
78 POSIX.1 specifies that nanosleep() should measure time against the
80 CLOCK_REALTIME clock. However, Linux measures the time using the
81 CLOCK_MONOTONIC clock. This probably does not matter, since the
82 POSIX.1 specification for clock_settime() says that discontinuous
83 changes in CLOCK_REALTIME should not affect nanosleep():
84 Setting the value of the CLOCK_REALTIME clock via clock_set‐
86 time() shall have no effect on threads that are blocked waiting
87 for a relative time service based upon this clock, including the
88 nanosleep() function; ... Consequently, these time services
89 shall expire when the requested relative interval elapses, inde‐
90 pendently of the new or old value of the clock.
91 Old behavior
93 In order to support applications requiring much more precise pauses
94 (e.g., in order to control some time-critical hardware), nanosleep()
95 would handle pauses of up to 2 ms by busy waiting with microsecond pre‐
96 cision when called from a thread scheduled under a real-time policy
97 like SCHED_FIFO or SCHED_RR. This special extension was removed in
98 kernel 2.5.39, hence is still present in current 2.4 kernels, but not
99 in 2.6 kernels.
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102 In Linux 2.4, if nanosleep() is stopped by a signal (e.g., SIGTSTP),
103 then the call fails with the error EINTR after the thread is resumed by
104 a SIGCONT signal. If the system call is subsequently restarted, then
105 the time that the thread spent in the stopped state is not counted
106 against the sleep interval.
107
109 clock_nanosleep(2), sched_setscheduler(2), sleep(3), timer_create(2),
110 usleep(3), time(7)
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113 This page is part of release 3.25 of the Linux man-pages project. A
114 description of the project, and information about reporting bugs, can
115 be found at http://www.kernel.org/doc/man-pages/.
116Linux 2009-01-19 NANOSLEEP(2)